CN104331113A - High-precision numerically-controlled constant current source - Google Patents

Abstract

The invention discloses a high-precision numerically-controlled constant current source, comprising a digital signal processor, a digital-analog conversion circuit, a constant current source circuit and a sampling circuit, wherein the general input-output interface of the digital signal processor is connected with the constant current source circuit through the digital-analog conversion circuit; the digital signal processor generates an output current according to a given value; the output current flows into the constant current source circuit after the digital-analog conversion executed by the digital-analog conversion circuit; the sampling circuit is connected between the constant current source circuit and the digital-analog conversion interface of the digital signal processor, acquires the actual value of the output current, and sends the actual value to the digital-analog conversion interface for digital-analog conversion; the digital signal processor calculates a deviation between the given value and the actual value, uses an integral separation PID (Proportion Integration Differentiation) algorithm to adjust the output current when the deviation is smaller than or equal to a threshold value, and uses a PD algorithm to adjust the output current when the deviation is greater than the threshold value.

Description

A kind of high precision numerical control constant-current source

Technical field

The present invention relates to control, regulation technology field, particularly a kind of high precision numerical control constant-current source.

Background technology

Along with the development of electronic technology, the expansion of digital circuit application, now society, intelligent product, digitizing have become a kind of trend that people pursue, the performance of equipment, price, development spaces etc. enjoy the concern of people, especially pay close attention to the most the precision of electronic equipment and degree of stability.The electronic equipment that performance is good, first be unable to do without stable power supply, stability of power supply is higher, equipment and peripheral condition more superior, so the life-span of equipment is longer.Based on this, the demand of people to numerical control steady current device is more and more urgent.

Modern industry field applies low ripple, high-precision constant current source more and more widely.Traditional constant current source adopts linear regulation and analog control mode, there is the shortcomings such as conversion efficiency is low, control accuracy is low, reliability is lower.

Summary of the invention

The present invention is directed to prior art above shortcomings, provide a kind of high precision numerical control constant-current source.The present invention is achieved through the following technical solutions:

A kind of high precision numerical control constant-current source, comprising: digital signal processor, D/A converting circuit, constant-current source circuit and sample circuit;

The universal input/output interface of digital signal processor connects constant-current source circuit by D/A converting circuit, and digital signal processor produces output current according to set-point, and output circuit carries out entering constant-current source circuit after analog to digital conversion through D/A converting circuit;

Sample circuit is connected between the analog to digital conversion interface of constant-current source circuit and digital signal processor, obtains the actual value of output current, and sends into analog to digital conversion interface and carry out analog to digital conversion;

Digital signal processor calculates the deviation of set-point and actual value, adopts separated integrator PID algorithm adjustment output current when deviation is less than or equal to a threshold value, adopts PD algorithm adjustment output current when deviation is greater than threshold value.

Preferably, separated integrator PID algorithm is expressed as:

$u\left(k\right)=K_{p}e\left(k\right)+\mathrm{\β}{K}_i\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)T+K_d[e\left(k\right)-e(k-1)]/T$

$\mathrm{\β}=\left\{\begin{array}{cc}1& \left|e\left(k\right)\right|\≤\mathrm{\ϵ}\\ 0& \left|e\left(k\right)\right|>\mathrm{\ϵ}\end{array}\right.$

Wherein, K _pfor scale-up factor, K _ifor integral coefficient, K _dfor differential coefficient, e (k) is deviate, and k is sampling sequence number, and T is the sampling period, and ε is threshold value.

Preferably, also comprise: button, display, the universal input/output interface of button and display linking number word signal processor, respectively in order to control figure signal processor and show in real time.

The invention provides high precision numerical control constant-current source, response is fast, and conversion efficiency is high, good reliability, and adaptive ability is strong, is convenient to later maintenance and functions expanding.By the correction of stable hardware circuit design and software, have a wide range of applications in the high-power constant current field such as communication system, electric system.

Accompanying drawing explanation

Shown in Fig. 1 is system chart of the present invention;

Shown in Fig. 2 is constant-current source circuit structure figure of the present invention;

Shown in Fig. 3 is D/A converting circuit structural drawing of the present invention;

Shown in Fig. 4 is power supply circuit construction figure of the present invention;

Shown in Fig. 5 is main flow chart of the present invention;

Shown in Fig. 6 is the system chart of PID controller;

Shown in Fig. 7 is the process flow diagram of integral separation PID controling algorithm of the present invention;

Shown in Fig. 8 is the given electric current of the present invention from the oscillogram of 255 milliamperes of saltus steps to 245 milliampere;

Shown in Fig. 9 is the given electric current of the present invention from the oscillogram of 345 milliamperes of saltus steps to 245 milliampere.

Embodiment

Below with reference to accompanying drawing of the present invention; clear, complete description and discussion are carried out to the technical scheme in the embodiment of the present invention; obviously; as described herein is only a part of example of the present invention; it is not whole examples; based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art obtain under the prerequisite not making creative work, all belongs to protection scope of the present invention.

For the ease of the understanding to the embodiment of the present invention, be further explained for specific embodiment below in conjunction with accompanying drawing, and each embodiment does not form the restriction to the embodiment of the present invention.

Hardware configuration of the present invention is main as shown in Figure 1, comprising: digital signal processor 1 (replacing with DSP below), D/A converting circuit 2, constant-current source circuit 3, sample circuit 4, liquid crystal display 5, clock circuit 7, keyboard 6 and reset circuit 8 etc.At input AC 220V, during 50HZ, export DC current 20mA ~ 2000mA, there is "+", "-" step by step modulating function, stepping 1mA, 10mA and 100mA can be realized; Can to arrange and display translation given value of current value, 0.5% of output current and set-point error≤set-point.This constant-current source circuit completes the setting of output current by button, and the electric current of output sends the ADC port of DSP inside back to after sampling circuit samples.By the comparison of DSP to sampled value and set-point, DSP carries out pid algorithm process according to result and obtains revising rear output signal.What realize electric current stablizes controlled output.

DSP is the control core of whole system of the present invention, has needed high-precision A/D conversion, display and control, algorithm process etc.According to the accuracy requirement of design, selected the TMS320F28335 type digital signal processor of TI company in the design, it is a Floating-point DSP controller.Compared with fixed DSP, the precision of this device is high, and cost is low, and power consumption is little, peripheral hardware integrated level high.Meanwhile, the YB12864ZB Chinese character image dot matrix lcd module be connected with DSP serial ports, the set-point of display translation electric current and step value.

High precision voltage controlled current source is the key of Numerical Controlled Current Source, and according to technical requirement, constant-current source circuit have employed the controlled constant-current source circuit of continuous setup type.As shown in Figure 2, by introducing the Current Negative Three-Point Capacitance of the degree of depth, Control of Voltage electric current is adopted to ensure precision.It is made up of comparison amplifier, Circuit tuning, sampling resistor and load, selects LF356 comparer, 8050 triodes and TIP41 Darlington transistor.Due to, the precision of constant-current source circuit is closely related with sampling resistor, selects the 1 Ω constantan-made resistances (temperature coefficient is 5 × 10-6/ DEG C) of high precision, Low Drift Temperature as sampling resistor in the design.

According to designing requirement output current scope 20 ~ 2000mA, stepping 1mA, namely resolution is 1mA, according to formula

$n=\mathrm{lo}{g}_2\frac{I_{\max }}{\mathrm{\ΔI}}={\log }_2\frac{2000\mathrm{mA}}{1\mathrm{mA}}\≈11---\left(1\right)$

Therefore the DAC chip TLC5618 of 12 is selected.Use+5V single power supply in design, select exemplary reference voltage Vref=2.048V, the resolution of D/A conversion is:

$V_D=\frac{V_{\mathrm{ref}}}{2^{12}}=\frac{2048}{4096}=0.5\mathrm{mA}---\left(2\right)$

D/A change-over circuit as shown in Figure 3.1,2,3 pins of its chips TLC5618 connect the control signal of DSP general-purpose interface respectively, and the data that the 4th pin exports are delivered to constant-current source circuit and processed, and reference voltage then by the adjustment of stabilivolt and potentiometer, meets design requirement.

The stability of feed circuit determines the stability of reference source, the i.e. stability of constant current source output current.These feed circuit adopt bridge full-wave rectifier, bulky capacitor filtering, three terminal regulator, provide ± 5V and the ± direct supply of 12V.TMS320F28335 chip needs the voltage of 3.3V and 1.9V, also has requirement, therefore adopt special power management chip TPS767D301 for DSP core voltage and the I/O port voltage order that powers on.DSP power pack circuit diagram as shown in Figure 4.

Main flow of the present invention adopts structured programing design method, after the initialization of master routine completion system, waits for key-press input, after completing set-point input, DSP provides corresponding output voltage control signal, is then changed and constant-current source circuit by D/A, realizes the output of electric current.The key controlled: DSP first produces output current according to given input, then combines the actual value that electric current is sent in sampling back to, calculates control deviation, then call corresponding pid algorithm process, complete the control of output current through DSP.Main flow as shown in Figure 5.

Classical PID controls to refer to and the ratio of deviation (P), integration (I) and differential (D) is formed controlled quentity controlled variable by linear combination, controls, as shown in Figure 6 to controlled device.Static difference is eliminated in the effect introducing integration in PID controls, and improves precision.Usually, when system starts or significantly increase and decrease sets, the relatively large deviation of short time can cause the integration of PID arithmetic to accumulate, and causes the overshoot of system.Therefore, there is employed herein integral separation PID controling algorithm.

In continuous-time domain, the expression formula of PID controller algorithm:

$u\left(t\right)=K_p[e\left(t\right)+\frac{1}{T_i}{\∫}_0^{t}e\left(t\right)\mathrm{dt}+T_d\frac{\mathrm{de}\left(t\right)}{\mathrm{dt}}]---\left(3\right)$

Wherein, set-point r (t) and real output value y (t) form control deviation e (t), i.e. e (t)=r (t)-y (t).

In formula (3): K _pfor scale-up factor, timely response can be made to system deviation; T _ifor integration time constant, for eliminating static difference, improve system without margin; T _dfor derivative time constant, reduce dynamic overshooting, improve dynamic perfromance.

By simulation control of PID algorithm, represent t continuous time with series of samples moment point kT, replace integration so that Rectangular Method numerical integration is approximate, replace differential so that single order backward difference is approximate, namely

$\left\{\begin{array}{c}t\≈\mathrm{kT},(k=\mathrm{0,1,2},...)\\ {\∫}_0^{t}e\left(t\right)\mathrm{dt}\≈T\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)\\ \frac{\mathrm{de}\left(t\right)}{\mathrm{dt}}\≈\frac{e\left(k\right)-e(k-1)}{T}\end{array}\right.---\left(4\right)$

Discrete PID expression formula can be obtained:

$u\left(k\right)=K_{p}e\left(k\right)+\frac{K_{p}T}{T_i}\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)+K_p{T}_d\frac{e\left(k\right)-e(k-1)}{T}=K_{p}e\left(k\right)+K_i\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)T+\frac{K_d}{T}[e\left(k\right)-e(k-1)]---\left(5\right)$

Wherein, T is the sampling period; K is sampling sequence number; and K _d=K _pt _dbe respectively integral coefficient and differential coefficient.

And integral separation PID controling algorithm refers to when control deviation is larger, cancel integral action; When control deviation is less, introduce integration control.As shown in Figure 7, the size of control deviation is decided by threshold size ε algorithm flow.

Therefore, the pid control algorithm of native system can be expressed as:

$u\left(k\right)=K_{p}e\left(k\right)+\mathrm{\β}{K}_i\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)T+K_d[e\left(k\right)-e(k-1)]/T$

$\mathrm{\β}=\left\{\begin{array}{cc}1& \left|e\left(k\right)\right|\≤\mathrm{\ϵ}\\ 0& \left|e\left(k\right)\right|>\mathrm{\ϵ}\end{array}\right.---\left(6\right)$

Through the experiment test in later stage, the threshold value of system is set in 10mA, has both effectively prevent the overshoot of system, in turn ensure that quick response.

Below by way of a test data, this law is verified:

Test adopts Keithley2000 type digital multimeter, AS2173 type ac millivoltmeter and Tektronix TDS1002 type digital oscilloscope.When load is 2 Ω, the test result of output current and ripple current is as shown in table 1.

Table 1

Test result: output current scope is 20mA ~ 2000mA.When load is 2 Ω, given practical measurement of current error is substantially within 0.5%, and ripple current is less than 0.2mA.

In order to test stepping controlling functions further, given electric current is set respectively from 255mA saltus step to 245mA, 345mA saltus step to 245mA two kinds of situations, respectively as shown in Figure 8, Figure 9.

Test result shows, integral separation PID controling algorithm achieves the effective control to system.When stepping is 10mA, control to export by PD algorithm; When stepping is 100mA, integral algorithm participates in controlling, and response fast, thus makes to reach set-point in the output current short time.

The present invention is control core with DSP (digital signal processing, digital signal processor), introduces integral separation PID controling algorithm, and adjustment in real time exports the electric current of setting.By pressing key assignments stepping and liquid crystal display step value and measured value.Actual test result shows, this electric power outputting current precision is high, good reliability, is applicable to high-power constant current application scenario.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claim.

Claims (3)

1. a high precision numerical control constant-current source, is characterized in that, comprising: digital signal processor, D/A converting circuit, constant-current source circuit and sample circuit;

The universal input/output interface of described digital signal processor connects described constant-current source circuit by described D/A converting circuit, described digital signal processor produces output current according to set-point, and output circuit carries out entering described constant-current source circuit after analog to digital conversion through described D/A converting circuit;

Described sample circuit is connected between the analog to digital conversion interface of described constant-current source circuit and described digital signal processor, obtains the actual value of described output current, and sends into described analog to digital conversion interface and carry out analog to digital conversion;

Described digital signal processor calculates the deviation of described set-point and described actual value, adopts separated integrator PID algorithm to adjust described output current when deviation is less than or equal to a threshold value, adopts PD algorithm to adjust described output current when deviation is greater than described threshold value.

2. high precision numerical control constant-current source according to claim 1, is characterized in that, described separated integrator PID algorithm is expressed as:

$u\left(k\right)=K_{p}e\left(k\right)+\mathrm{\β}{K}_i\underset{j=0}{\overset{k}{\mathrm{\Σ}}}e\left(j\right)T+K_d[e\left(k\right)-e(k-1)]/T$

$\mathrm{\β}=\left\{\begin{array}{cc}1& \left|e\left(k\right)\right|\≤\mathrm{\ϵ}\\ 0& \left|e\left(k\right)\right|>\mathrm{\ϵ}\end{array}\right.$

Wherein, K _pfor scale-up factor, K _ifor integral coefficient, K _dfor differential coefficient, e (k) is described deviate, and k is sampling sequence number, and T is the sampling period, and ε is described threshold value.

3. high precision numerical control constant-current source according to claim 1, it is characterized in that, also comprise: button, display, described button and described display connect the universal input/output interface of described digital signal processor, respectively in order to control described digital signal processor and to show in real time.